Recently, with the popularization of digital cameras, mobile phones with camera function, and the like, the market of solid-state imaging devices has significantly been expanded. Increase in resolution achieved by cell-size miniaturization dramatically improves image quality of cameras.
In such a solid-state imaging device, for example, a charge-coupled device (CCD) or metal-oxide-semiconductor (MOS) image sensor, a plurality of pixels having light-receiving portions are two-dimensionally arrayed to convert incident light traveled from an object into electrical signals. Sensitivity of the solid-state imaging device is defined by a magnitude of the electrical signals which are outputted from light-receiving elements according to an amount of the incident light. It is therefore important to guide the incident light certainly to reach the light-receiving elements to improve the sensitivity.
In each pixel in the conventional common solid-state imaging devices, light incident on a microlens passes through a color filter, which is a red filter (R), a green filter (G), or a blue filter (B), for color separation and then converted by a light-receiving portion to electrical signals.
However, such a conventional common color filter absorbs the incident light except transmitted light. Therefore, approximately only 25% of the incident light can be converted to electrical signals. In short, light use efficiency is low. Therefore, the solid-state imaging device with such conventional absorptive color filters has a difficulty of improving light use efficiency.
In order to solve the above problem, as disclosed in Patent Literature (PTL) 1, there has been proposed a technique in which a medium having a refractive index that periodically varies is used as a dispersive element so as to improve light use efficiency of a solid-state imaging device. According to this technique, incident light is dispersed to different wavelength bands, and the dispersed lights are guided to respective corresponding light-receiving portions to be converted to electrical signals. As a result, light use efficiency is improved in comparison with the conventional method using color filters.